Tactile device

ABSTRACT

The invention relates to a tactile device provided with a number of fluid elements ( 1 ) containing an electrically conducting fluid ( 3, 4 ). The fluid level in each element is movable by actuator means (V,  6 ) applying a electric power to said fluid elements. Each fluid element is in contact with the fluid for perception of the fluid level by a user. The fluid elements comprise capillary tubes ( 2 ) in which the fluid level is movable as a result of electro-capillary pressure.

The present invention relates to a tactile device provided with a numberof fluid elements containing an electrically conducting fluid, the fluidlevel in each element being movable, actuator means for moving the fluidlevel of a number of selected fluid elements by applying an electricforce to said fluid elements, wherein each fluid element is providedwith a tactile element that is in contact with the fluid for perceptionof the fluid level by a user.

In general tactile devices are arranged to transfer information byactivating the user's feeling of touch. Several types of tactile devicesare known in practice. For example one type of tactile devices isarranged to provide force-feedback in joysticks, mice, control pads andthe like or to vibrate mobile phones. Another type of tactile devices isfor instance applied in brail reading machines to transfer more complexinformation.

A device of the type as described above is known from GB 2 212 336. Theknown device comprises a number of fluid chambers filled with liquidcrystal. Each of the chambers comprises a pair of sleeves acting aselectrodes for applying an electric field to the fluid in order tochange the fluid level using the Maxwell-Faraday effect. A piston pinfloating on the fluid acts as a feeler indicating the fluid level. Theknown device forms part of a brail reading machine.

The known device has the disadvantage that it consumes a lot of electricpower. Furthermore the movable mechanical pins appear to be noisy. Inpractice the known device has shown lack of reliability combined withhigh costs.

It is an object of the invention to provide a device of the type asdescribed above that solves these problems.

The device according to the invention is therefore characterized in thatthe fluid elements comprise capillary tubes in which the fluid level ismovable as a result of electro-capillary pressure.

Application of capillary tubes using electro-capillary pressure allowsthe fluid level to be changed sufficiently with a minimal amount ofelectric power. The device according to the invention may comprise asmany fluid elements as necessary depending on the application and stillbe dynamic and easily programmable. Since the size of the fluid elementscan be kept small, a total of 100×100 cells can fit into and can thusaddress the palm of a hand.

In a first preferred embodiment of the tactile device according to theinvention the actuator means are arranged to vibrate the tactile elementfor a predetermined period of time when the fluid level has changed to anew position. The feeling of touch of the user is thereby activated in anatural way thereby improving the quality of information transfer to theuser.

According to a further preferred embodiment the tactile elementcomprises a diaphragm of flexible material. The diaphragm can be movedrapidly and silently allowing a reliable and fast transfer ofinformation without unwanted noise.

Preferably the diaphragm is provided with at least one contact spot toenhance the tactile feeling of the user.

In another preferred embodiment one or more capillary tubes are providedat the opposite end with a further diaphragm of flexible material. Thecapillary tubes are now separated so crosstalk is effectively avoided.

In yet another preferred embodiment the actuator means are arranged forsetting the fluid level of a number of selected capillary tubes at apredetermined prestressed level and the tactile device further comprisesdetector means which are arranged for detecting a change of fluid levelin the selected capillary tubes. In this embodiment the tactile devicemay advantageously also function as a sensor picking up signals from theuser.

In a practical embodiment the detector means are arranged for detectinga change of electric capacitance in the selected capillary tubes. Usingthis type of detector means the tactile device can advantageously bebuilt in a compact form.

According to a further preferred embodiment one or more capillary tubescomprise a first fluid and a second fluid having different electricalconductivities, the fluids being essentially immiscible. This embodimentallows a voltage-dependent pressure to be applied to the capillary tubesto control the degree of movement of the tactile element. In a furtherdetailed embodiment thereof either the first or the second fluid iselectrically conducting and the other fluid, the second or first fluid,respectively, is electrically insulating. The range of movement isthereby maximal resulting in optimal sensitivity of the tactile device.

According to a practical embodiment the actuator means comprise anelectrical power source and a number of electrodes. In these embodimentsthe actuator means are formed by a minimal amount of components that arereliable and relatively cheap.

Preferably the detector means comprise a voltage source and a currentmeasurement device. Since a voltage source is already present only acurrent measurement device needs to be added to realize the sensorfunction provided for by the detector means.

Preferably one or more capillary tubes comprise at least one electrodethat is attached to the wall of the capillary tube.

The invention will be further explained by means of the attacheddrawing, in which:

FIG. 1 schematically shows a preferred embodiment of a fluid element aspart of the device according to the invention in a first state;

FIG. 2 schematically shows the fluid element of FIG. 1 in a secondstate;

FIG. 3 schematically shows a preferred embodiment device according tothe invention.

In all Figures equal objects are denoted by equal reference numerals.

FIG. 1 and FIG. 2 schematically show a preferred embodiment of a fluidelement 1 as part of the device according to the invention. Fluidelement 1 comprises a capillary tube 2 filled with a first electricallyconducting fluid 3. On top of the conducting fluid lies an electricallyinsulating fluid 4. Fluids 3 and 4 are essentially immiscible, which isindicated by means of the fluid/fluid meniscus 5. In an alternativeembodiment fluid 3 is electrically insulating, while fluid 4 iselectrically conducting. Examples of suitable electrically conductingfluids are aqueous solutions. Examples of suitable electricallyinsulating fluids are a gas or a nonpolar oil.

Actuator means are provided for applying electric power to the capillarytube 2. As a result thereof an electro-capillary pressure is introducedcausing a change in the fluid level of the capillary tube. The actuatormeans comprise an electrical power source V and a number of electrodes6. In the preferred embodiment shown one electrode 6 is integrated inthe wall of each capillary tube 2. The electrode 6 comprises a layer ofconducting material. An insulating layer as well as a hydrophobiccoating may be added thereto.

Each capillary tube 2 is provided with a tactile element 7 that is incontact with the fluid for perception of the fluid level by a user. Thetactile element comprises a diaphragm 7 of flexible material on top ofthe fluid essentially closing the capillary tube 2 at one end thereof.In the preferred embodiment the diaphragm 7 comprises a flexible foil. Asuitable material is a flexible plastic. The flexible foil is glued orsealed to the walls of the capillary tube. The diaphragm 7 is providedwith a contact spot 8 of a more rigid material, for instance a morerigid plastic. The contact spot 8 is smaller than the diaphragm 7 andmay have any shape, such as a dot or a disc.

When by means of the power source V and the electrode 6 an electricpower is applied to the capillary tube 2, an electro-capillary pressureis introduced by means of which the fluid level can be manipulated. Achange of fluid level directly results in a change of position of thediaphragm 7. As an illustration thereof two different situations areshown in FIGS. 1 and 2. In FIG. 1 the capillary tube 2 is shown in afirst state, wherein the diaphragm 7 is bent upwards. In FIG. 2 thecapillary tube 2 is shown in a second state, wherein the diaphragm 7 isbent downward. The diaphragm 7 functions as a feeler transferringinformation to a user based on the activation of the feeling of touch.

It is noted that the phenomenon of electro-capillary pressure is knownper se in the field. In short the capillary pressure on the fluid/fluidmeniscus 5 is determined by the difference between two interfacialtensions. On the one hand the tension of the interface between the wallof the capillary tube 2 and the conducting fluid 3 and on the other handthe tension of the interface between the wall of the capillary tube 2and the insulating fluid 4. The tension influences the position of thefluid/fluid meniscus 5 and therefore also the position of the diaphragm7. For a more detailed discussion of the phenomenon of electro-capillarypressure reference is made to the article “Fluid Control in MultichannelStructures by Electro capillary Pressure”, by Prins et al, Science,Volume 291, 12 Jan. 2001, which is incorporated herein by reference.

The actuator means V, 6 are arranged to vibrate the diaphragm 7 for apredetermined period of time. Typically the vibration is applied whenthe diaphragm 7 has reached another state due to a change in fluidlevel. The vibration activates the feeling of touch in a more naturalway. Many suitable actuator means for this task are available to aperson skilled in the art, such as means for oscillating the voltageprovided by the power source V during said time period.

FIG. 3 schematically shows a device 10 comprising an array of capillarytubes 2 according to the invention. The position of each of thediaphragms 7 depends on the voltage applied to the correspondingcapillary tube 2. In the example shown device 10 consists of one row ofonly eight capillary tubes 2. It will be understood that the number andconfiguration of the capillary tubes in the device according to theinvention may vary. Preferably the capillary tubes in the device arearranged in a matrix configuration. In practice the number of capillarytubes is limited only by practical restrictions, such as the size of thedevice and the number of electrical connections. Since the fluidelements comprise micro channels, such as capillary tubes, of inherentlysmall size, the device according to the invention may comprise a largenumber of fluid elements and still be easy to handle. A threshold-likebehaviour of the capillary tubes can be achieved by changing thephysical characteristics of the capillary tubes. By designing thecapillary tubes such that the physical characteristics thereof inducethreshold-like behaviour, extra components, such as transistors ordiodes, become redundant. This further reduces the size of the deviceaccording to the invention. In published international patentapplication WO 02/39462 A2, which is incorporated herein by reference,an example of a device comprising a matrix of capillary tubes havingsegmented electrodes showing a threshold-like behaviour is described.

The number of electrical connections can be advantageously reduced byapplying the method of matrix addressing that is known per se in thefield. If every capillary is connected to an individual wire, the numberof required electronic control elements scales with N². A well-knownmethod to reduce the number of control elements to a number of the orderN, is by matrix addressing. Matrix addressing means that rows (indexedi, iε{1, . . . , N}, voltage V_(i)) are activated one-by-one while theprogramming signals are placed on column wires (indexed j, jε{1, . . . ,N}, voltage V_(j)). In order to apply matrix addressing in a tactiledevice an electrical matrix structure is needed in every capillary tube,i.e. every capillary tube (i, j) needs to be connected to voltages V_(i)and V_(j). In the cited WO 02/39462 A2 three examples thereof are shown.

In addition to the actuator function described above the deviceaccording to the invention can also function as a sensor. Theretodetector means comprising a voltage source and a current measurementdevice I are connected to each capillary tube 2 for detecting a changeof electric capacitance. When the position of the diaphragm 7 is changedactively, for instance by pressure exerted thereon by a user, this willresult in a change of electric capacitance in the correspondingcapillary tube 2, which will be detected by the detector means. Theelectrical power source V can serve as the voltage source for instanceproviding a voltage ripple or a voltage pulse. By measuring the currentusing device I any change of electric capacitance can be detected.Information can now be transferred to the device simply by exertingpressure on the diaphragm 7 of one or more selected capillary tubes 2.The diaphragms need to be prestressed to a sufficient extent that canelegantly be provided for by the actuator means. Detector means fordetecting a change of electric capacitance are described in more detailin the articles: “Contact angles and wetting velocity measuredelectrically”, by H. J. J. Verheijen and M. W. J. Prins, Rev. Sci.Instr. 70(9), 3668-73 (1999), and ‘Fluid control in multichannelstructures by electro capillary pressure’, by M. W. J. Prins, W. J. J.Welters, and J. W. Weekamp, Science 291(5502), 277-280 (2001). Manysuitable alternative detector means, such as means for optical detectionof deformation of the diaphragm 7 or the meniscus 5, are also availableto a person skilled in the art.

In device 10 each capillary tube 2 is closed at the bottom by means of asecond diaphragm 9. Diaphragm 9 may have the same characteristics asdiaphragm 7. The capillary tubes 2 are thus separate entities andhydrostatic crosstalk is prevented sufficiently. Alternatively, thecapillary tubes may use a shared reservoir of the first fluid. Althoughthe production costs will probably be lower, crosstalk is inevitablemaking the alternative embodiment useful only for certain less criticalapplications. In both embodiments a certain under pressure in the fluidis useful, such that the diaphragm 9 has not yet reached its most upwardbent position. Various means for creating under pressure are availableto a person skilled in the art, such as a hydrophobic coating on thewall of the capillary tubes.

In general the device according to the invention refers to a tactiledevice using capillary tubes, in which the fluid level is to bemanipulated by electro-capillary pressure, to transfer information. Thetactile device either functions as an actuator or as a sensor or as acombination thereof.

The tactile device can be used for a wide variety of applications someof which will be mentioned here. A first application is as acommunication device, especially to provide additional information in asituation where the visual system is already overloaded, for instance inairplanes, operating rooms, vehicles etc. A second application is avirtual reality device, such as a glove that provides full tactilesensation over the palm and fingertips of the user. Other applicationsmay be a telerobotic manipulator or an electronic book for the visuallyimpaired.

The invention is of course not limited to the embodiments described orshown, but generally extends to any embodiment, which falls within thescope of the appended claims as seen in the light of the abovedescription and drawings.

1. A tactile device provided with a number of fluid elements, each fluidelement containing a first fluid and a second fluid having differentelectrical conductivities and being essentially immiscible, a fluidlevel between the first fluid and the second fluid in each element beingmovable, and actuator means for moving the fluid level of a number ofselected fluid elements by applying an electric force to said fluidelements, wherein each fluid element is at one end provided with atactile element that is in contact with the fluid for perception of thefluid level by a user, characterized in that the fluid elements compriseone or more capillary tubes in which either the first fluid or thesecond fluid is electrically conducting and the other fluid, the secondor the first fluid, respectively, is electrically insulating, and thefluid level is movable as a result of electro-capillary pressure.
 2. Atactile device according to claim 1, wherein the actuator means arearranged to vibrate the tactile element for a predetermined period oftime.
 3. A tactile device according to claim 1, wherein the tactileelement comprises a diaphragm of flexible material.
 4. A tactile deviceaccording to claim 3, wherein the diaphragm is provided with at leastone contact spot.
 5. A tactile device according claim 1, wherein saidone or more capillary tubes are provided with a further diaphragm offlexible material at an end thereof which is opposite to the one endprovided with the tactile element.
 6. A tactile device according toclaim 1, wherein the actuator means comprise an electrical power sourceand a number of electrodes.
 7. A tactile device provided with a numberof fluid elements containing an electrically conducting fluid, a fluidlevel in each element being movable, actuator means for moving the fluidlevel of a number of selected fluid elements by applying an electricforce to said fluid elements, wherein each fluid element is at one endprovided with a tactile element that is in contact with the fluid forperception of the fluid level by a user, characterized in that the fluidelements comprise capillary tubes in which the fluid level is movable asa result of electro-capillary pressure, wherein the actuator means arearranged for setting the fluid level of a number of selected capillarytubes at a predetermined prestressed level and wherein the devicefurther comprises detector means that are arranged for detecting achange of fluid level in the selected capillary tubes.
 8. A tactiledevice according to claim 7, wherein the detector means are arranged fordetecting a change of electric capacitance in the selected capillarytubes.
 9. A tactile device according to claim 7, wherein one or morecapillary tubes comprise a first fluid and a second fluid havingdifferent electrical conductivities, the fluids being essentiallyimmiscible.
 10. A tactile device according to claim 9, wherein eitherthe first fluid or the second fluid is electrically conducting and theother fluid, the second or first fluid, respectively, is electricallyinsulating.
 11. A tactile device according to claim 7, wherein thedetector means comprise a voltage source and a current measurementdevice.
 12. A tactile device according to claim 7, wherein the actuatormeans are arranged to vibrate the tactile element for a predeterminedperiod of time.
 13. A tactile device according to claim 7, wherein thetactile element comprises a diaphragm of flexible material.
 14. Atactile device according to claim 13, wherein the diaphragm is providedwith at least one contact spot.
 15. A tactile device according claim 7,wherein said one or more capillary tubes are provided with a furtherdiaphragm of flexible material at an end thereof which is opposite tothe one end provided with the tactile element.
 16. A tactile deviceprovided with a number of fluid elements containing an electricallyconducting fluid, a fluid level in each element being movable, actuatormeans for moving the fluid level of a number of selected fluid elementsby applying an electric force to said fluid elements, wherein each fluidelement is at one end provided with a tactile element that is in contactwith the fluid for perception of the fluid level by a user,characterized in that the fluid elements comprise capillary tubes inwhich the fluid level is movable as a result of electro-capillarypressure, wherein the actuator means comprise an electrical power sourceand a number of electrodes, wherein one or more capillary tubes compriseat least one electrode that is attached to the wall of the capillarytube.
 17. A tactile device according to claim 16, wherein the detectormeans are arranged for detecting a change of electric capacitance in theselected capillary tubes.
 18. A tactile device according to claim 16,wherein one or more capillary tubes comprise a first fluid and a secondfluid having different electrical conductivities, the fluids beingessentially immiscible.
 19. A tactile device according to claim 16,wherein either the first fluid or the second fluid is electricallyconducting and the other fluid, the second or first fluid, respectively,is electrically insulating.
 20. A tactile device according to claim 16,wherein the detector means comprise a voltage source and a currentmeasurement device.